238 replies to this topic

[John Fitzgerald]

Back on August 19, I had good seeing, and saw a definite split on this one with my 6" f/8 apo at 243x, using a 5mmTV Delite eyepiece.

 

Cyg SAO 68695 RA 19 41 15 Dec +30 43 17 Desig: BU 145 AB, PA 272, Sep 0.85", m 7.4, 9.09.  

[Nucleophile]

Back on August 19, I had good seeing, and saw a definite split on this one with my 6" f/8 apo at 243x, using a 5mmTV Delite eyepiece.

 

Cyg SAO 68695 RA 19 41 15 Dec +30 43 17 Desig: BU 145 AB, PA 272, Sep 0.85", m 7.4, 9.09.  

 

That's a fine instrument  you have there, John.  Nice result!

[columbidae]

From a few nights ago, during yet another hot and hazy night in S. Texas.  

 

BU 472 - 0.75", both mag 8.8

ADS 769 - 0.7", both mag 9.2  (love those even doubles)

BU 155 AB - 0.67", mags 7.4, 8.1

STF 2783 - 0.65", mags 7.7, 8.1

ADS 756 AB - 0.58", mags 8.3, 9.2

 

And, while being the furthest separated sub-arcsecond pair of the night, the most spectacular of them all:

 

HU 765 - 0.8", mags 9.3, 9.6, which combine as the secondary of STF 2764, 7" away from the 8.3 mag primary - a very pretty, well balanced, and close triple!  Very striking with nearly perpendicular PAs and a 10x difference in separation.

[R Botero]

Great session Columbidae. I need to check HU765. 
 

Roberto

[VanJan]

STF 2764/HU 765 - White, bluish, bluish. 11th magnitude companion p, slightly n. 250X  20cm reflector  October, 2022

[Nucleophile]

VanJan and Columbidae:  those are some fine targets to try.

 

I also like the Doubles of ~Equal Brightness (DEBs), especially those that cross from Rayleigh at one aperture to Dawes at another--gives me a chance to play around with my on-axis masks.  

[columbidae]

A brighter (and more well-known) duo from last night:

 

44 Boo, STF 1909: 0.47" (est.), mags 5.2, 6.1

Eta CrB, STF 1937AB: 0.57" (est.), mags 5.6, 6

 

Kind of annoyingly bright for close splitting in a 12", but each pair's numerous diffraction rings can't hide the black space in between the spurious disks.  (At least when the whole pattern stopped wobbling for a bit.)  I figured it'd probably be one of the last chances I'd get at the pair this season, so I went for them despite being at the dark site and having a list of other things to go for.

 

If you're a fan of the appearance of double stars in refractors, a sketch of what I saw would probably disgust you, but a split's a split. 

[flt158]

What are your magnifications for all these wonderful doubles, Columbidae?

I'm sure there are seriously high!  

 

Best regards from Aubrey.  

[columbidae]

Most of my close doubles are split at 381x, with my 4mm eyepiece; it's about 30x per inch in my scope, so high, but not as high as it could be.  I have a cheap 2x barlow (with a 1.5x option) that I sometimes use, but it usually isn't worth the extra magnification.  The seeing is rarely good enough to support 500x and up, and it doesn't work with my coma corrector, which is essential for maintaining good Airy patterns across the field of view.

 

About all but maybe two of the doubles I've split are still above the Rayleigh criterion in my scope, so such a "low" magnification might be a little limiting, but I'll take what I can get. 

[columbidae]

Tonight was more of a carbon star night, but there's always a double or two along the way:

 

• BU182 - 0.73", mags 8.7, 9.1 - "nicely dim, even, with ample space at 381x" 
• STT413AB (Lambda Cygni) - 0.91", mags 4.7, 6.3 - "easy but fuzzy"  A combination of it being lower in the sky and a mirror in need of cleaning - the brighter pairs aren't very forgiving of either.  Kind of strange seeing it look nothing like the sketches from folks with smaller apertures; the secondary is very "well-fed" in my scope.
• STT28 - 0.84", mags 7.6, 8.8 - a moderately unequal pair sitting nicely side by side
• STF13 - 0.96", mags 7.0, 7.1 - "even, bright"  Definitely recommend this one if you're looking for a sub-arcsecond pair to try, provided you aren't too far south.

[flt158]

 

Tonight was more of a carbon star night, but there's always a double or two along the way:

 

• BU182 - 0.73", mags 8.7, 9.1 - "nicely dim, even, with ample space at 381x" 
• STT413AB (Lambda Cygni) - 0.91", mags 4.7, 6.3 - "easy but fuzzy"  A combination of it being lower in the sky and a mirror in need of cleaning - the brighter pairs aren't very forgiving of either.  Kind of strange seeing it look nothing like the sketches from folks with smaller apertures; the secondary is very "well-fed" in my scope.
• STT28 - 0.84", mags 7.6, 8.8 - a moderately unequal pair sitting nicely side by side
• STF13 - 0.96", mags 7.0, 7.1 - "even, bright"  Definitely recommend this one if you're looking for a sub-arcsecond pair to try, provided you aren't too far south.

 

 

 

Tonight was more of a carbon star night, but there's always a double or two along the way:

 

• BU182 - 0.73", mags 8.7, 9.1 - "nicely dim, even, with ample space at 381x" 
• STT413AB (Lambda Cygni) - 0.91", mags 4.7, 6.3 - "easy but fuzzy"  A combination of it being lower in the sky and a mirror in need of cleaning - the brighter pairs aren't very forgiving of either.  Kind of strange seeing it look nothing like the sketches from folks with smaller apertures; the secondary is very "well-fed" in my scope.
• STT28 - 0.84", mags 7.6, 8.8 - a moderately unequal pair sitting nicely side by side
• STF13 - 0.96", mags 7.0, 7.1 - "even, bright"  Definitely recommend this one if you're looking for a sub-arcsecond pair to try, provided you aren't too far south.

 

Delightful report from you, Columbidae!

There are many fans of Lambda Cygni, as I am sure you are aware. 

I required 280x to see a black gap a few years ago.

Only recently did I split STF 13 (in Cepheus) at the same magnification. 

 

I'm sorry I haven't been reporting on double stars lately. 

I had set up my WO 158mm apo last night (Friday 29th October).  

But as soon as Sol setted, the dreaded high clouds arrived. 

Even the full Moon was shrouded in this same cloud. 

 

2023 is definitely one of the worst for clear skies over here in Ireland. 

I've only had 28 observing sessions. 

 

If it's my God's will, clearer skies will return. 

 

And on that note, best regards from Aubrey.  

[columbidae]

Seeing conditions last week (unlike the clouds this week) were decent, but I was surprised when I checked the separations on a few close pairs. 

 

• BU393 - 0.67", mags 6.9, 8.4 - Pretty tough, but I'm unsure about this one; the last recorded observation in the WDS is from 1991, 32 years ago.  Anyone know of any other sources to crosscheck from?  (Or want to follow up with an observation of their own?) 
• STT20AB - 0.63", mags 6.1, 7.2 - Grade 3 orbit in WDS, so it's pretty likely this is the correct separation. 
• BU303 - 0.46", mags 7.3, 7.6 - This pair was an easier split than BU393 - I don't know if it's because of the smaller magnitude difference (didn't seem like it to my eyes) or what.  The last observation is from 2018, but there's not a whole lot of other information on this one in the WDS either, so who knows.
• STT500 - 0.38", mags 6.1, 7.4 - This one has a Grade 4 orbit in the WDS catalog, so it's a bit more sure than the ones with few observations.  Still have a hard time personally believing it though; I didn't think the seeing was that good.  Maybe I'm getting better at picking out the pattern in the fleeting moments of calm.  There certainly weren't any picture perfect Airy disks this session.

 

Summer is definitely better here for good seeing, but between the bugs and the oppressive nighttime heat you definitely pay for it.

[fred1871]

Thought I'd look up the numbers on BU 393 (00 18.3 -21 08). The 1991 measure turns out to be by Tycho, and is slightly aberrant from the probable true numbers. If you look up the 4th Interferometric Catalogue you'll find that other measures in the period were different - making it slightly closer than Tycho gives.

 

It's been a slowly widening pair as the WDS entry suggests. In 1989 Hartkopf with 4-metre scope and using speckle got 0.626" and 24.1 for PA. Hipparcos in 1991 found 0.624" and 24 for PA. Hartkopf again, two measures in 1991, separations 0.619" and 0.623". The small variations are from the usual slight errors of measuring, notably smaller than older methods such as bi-filar micrometer.

 

So the more accurate measure would be 0.62" for 1991. I've examined many hundreds of doubles measures in this period around the time of Hipparcos/Tycho measuring, and compared the often differing TYC and HIP numbers with speckle measures, which are numerous in the period from a deliberate program of measuring for comparison of satellite with ground-based measures. Where TYC and HIP differ, it's almost always that HIP is better for close matching of speckle measures, and Tycho also in a surprising number of cases is not consistent with the long-term trend, as evaluated (where possible) to include post-1991 measures.

 

For a more recent measure than 1991 I'd suggest checking for Gaia DR3 data, which would enable a calculation of separation and angle for the date of the Gaia measures, about 25 years after Hipparcos, to show if BU 393 continued to widen subsequently.

[Nucleophile]

Seeing conditions last week (unlike the clouds this week) were decent, but I was surprised when I checked the separations on a few close pairs. 

 

• BU393 - 0.67", mags 6.9, 8.4 - Pretty tough, but I'm unsure about this one; the last recorded observation in the WDS is from 1991, 32 years ago.  Anyone know of any other sources to crosscheck from?  (Or want to follow up with an observation of their own?) 
• STT20AB - 0.63", mags 6.1, 7.2 - Grade 3 orbit in WDS, so it's pretty likely this is the correct separation. 
• BU303 - 0.46", mags 7.3, 7.6 - This pair was an easier split than BU393 - I don't know if it's because of the smaller magnitude difference (didn't seem like it to my eyes) or what.  The last observation is from 2018, but there's not a whole lot of other information on this one in the WDS either, so who knows.
• STT500 - 0.38", mags 6.1, 7.4 - This one has a Grade 4 orbit in the WDS catalog, so it's a bit more sure than the ones with few observations.  Still have a hard time personally believing it though; I didn't think the seeing was that good.  Maybe I'm getting better at picking out the pattern in the fleeting moments of calm.  There certainly weren't any picture perfect Airy disks this session.

 

Summer is definitely better here for good seeing, but between the bugs and the oppressive nighttime heat you definitely pay for it.

I should be able to give BU 393 a shot in the near future with my 8 inch reflector.  I have not observed this double as yet is seems.  I agree with Fred's analysis of the historical record.  Unfortunately, this double is an example of Gaia not detecting the secondary, so we don't have that (more recent) data point.  An independent measure is in order.  In the meantime, a comparative observation against congeneric candidates should shed some light.

 

According to my resolution calculator, BU 393 should remain unresolved when viewed on a night of good conditions (using my 8 inch instrument) if the separation is still around 0.62".  However, a rho value of 0.65" should be resolvable.  It will likely take several cracks at it to be certain.

 

STT 20AB has my interest as well.  Thanks for sharing these.

 

PS:  Gaia doesn't detect the companion for STT 20AB either.  I wonder if this is a part of the sky not scanned well by the satellite?

Edited by Nucleophile, 16 November 2023 - 06:28 PM.